vroland
commented
4 years ago That's good to hear ;) Not all things here where conscious decisions, sometimes I just went with what worked for me. But some things I can explain:
- Yes, I should update that some time... :sweat_smile:
- The IRLML6402 (Q1) is actually quite small (SOT-23 package). These big things are all LDOs.
- Mainly because I didn't optimize that much for size ;) But another reason is head dissipation and current output (0.1A vs 1.5A): At least according to the datasheet, the display can have large current spikes when powered on. And of course, normally you will disable power as soon as the drawing is done. But if you don't, such a small regulator may not handle generated heat, which can be significant when dropping from 22V to 15V. But you're welcome to try it :)
- The first version of the PCB actually used the WROOM-Module and the driver itself does not require the additional memory, but for most applications you'll need it. For the 9.7" display, the internal memory cannot even store a full framebuffer, much less two as used in the terminal application.
- The potentiometer is the variable resistor feeding into the amplifier for the VCOM voltage. Unfortuately, this voltage varies a lot, even for displays of the same type and is quite important for the output quality. So I think a trimmer is really needed here.
- I used the 4094 because it has an additional output register, which holds the old state while the internal shift register is updated. With the 595 you can only set the outputs to high-impedance, which would deactivate the switching power supply for the display every time I change a value in the register.
- As in 3. I have concerns about output power, especially if you power the display from 3.3V. This might be alleviated in the newest revision (see #3, #6) as you can also power the display via 5V, but I don't want to be forced to actually have 5V available. But maybe there is a more efficient, package-compatible regulator? Or another way to reconcile those needs?
I hope that answers some of your questions. I'm always open for suggestions and improvements, I'm only starting to learn about electronics myself :)
mcer12
simonrus
mmib
holgerlembke
Hi @vroland I love this and I am eager to make this thing! I plan on making it as compact as possible and also as cheap as possible, so I have some questions. Hope this is the right place to ask those... 1) I struggle with the BOM as the components are not marked with designators according to the schematic. Would it be possible for you to update the bom with component numbers? 2) in schematic IRLML6402 is used but it seems large mosfet is used on the pictured board (or is that a different component?). Is that just due to newer schematic revision? 3) Is there a reason why such a large regulators are used? There seems to be quite a few alternatives in SOT-89 like: https://lcsc.com/product-detail/New-Quadratic-Unclassified-Data_MDD-Microdiode-Electronics-78L15_C414028.html 4) Is ESP-WROVER required for its larger memory or can usual ESP-WROOM-32 be used? 5) I don't see the potentiometer in the schematic, also is it possible to provide resistance values for each display type? 6) Any particular reason why 74HC4094 is used instead of more widely available 74HC595? I see there are some differences between the two. 7) I see AMS1086CD-3.3 is used in BOM and LT1086 in the schematic, both of which have very large quiescent current. I use HT7333 in my ESP projects without problems. Maybe separate regulators for the display and the ESP would make sense? It would also be possible to easilly cut power to the display circuitry that way when the refresh is done to save more power.
Please don't take these questions as nitpicking on your awesome project, it's just me being OCD. I want to optimize everything as much as possible so it can be used in compact low power projects.